The present invention relates to a catalyst for use in producing acetic acid, a process for producing the catalyst and a process for producing acetic acid using the catalyst, which are used in the production of acetic acid from ethylene and oxygen by a single-stage catalytic reaction.
For producing acetic acid, a method of oxidizing acetaldehyde, a method of reacting methanol and carbon monoxide and a method of oxidizing liquid paraffin are conventionally used in practice.
The method for producing acetic acid from ethylene through single stage is advantageous in many points in view of the industrial production process and profitability and a large number of techniques have been proposed thereon. Examples thereof include a liquid phase single-stage oxidation process using an oxidation-reduction catalyst of metal ion pair such as palladium and cobalt and/or iron (see, French Patent No. 1,448,361), and a gas phase single-stage oxidation process using a catalyst comprising palladium-phosphoric acid or sulfur-containing modifying agent (see, Japanese Unexamined Patent Publications No. 47-13221 and No. 51-29425), a catalyst comprising a palladium salt of certain kinds of heteropolyacids (see, Japanese Unexamined Patent Publication No. 54-57488) or a catalyst comprising a 3-group system oxygen compound (see, Japanese Unexamined Patent Publication No. 46-6763).
In recent years, a process for producing acetic acid from ethylene and oxygen through a gas phase single stage using a catalyst comprising metal palladium and at least one compound selected from heteropolyacids and/or salts thereof (see, Japanese Unexamined Patent Publications No. 7-89896 and No. 9-67298) has been proposed. According to the process using this catalyst, the acetic acid can be obtained in a relatively high yield.
Particularly important matters in industry to take account of in practicing the reaction using such a catalyst are the requirements that the catalyst has high activity, the change in the catalytic activity by aging is as small as possible and the selectivity of acetic acid is good.
Those conventionally proposed methods where acetic acid is obtained from ethylene and oxygen through a gas phase single stage using a catalyst comprising palladium and at least one compound selected from heteropolyacids and/or salts thereof are satisfied in view of practice in an industrial scale, however, if the catalytic activity can be more improved, this is economically advantageous.
It is an object of the present invention to provide a higher performance catalyst, a process for producing the catalyst, and a process for producing acetic acid using the catalyst, which are used in the process for producing acetic acid from ethylene and oxygen by a gas phase single-stage reaction using a catalyst comprising palladium and at least one compound selected from heteropolyacids and/or salts thereof.
For attaining the above-described object, the present inventors have made extensive investigations to elevate the performance of the catalyst comprising palladium and at least one compound selected from heteropolyacids and salts thereof, for use in the production of acetic acid from ethylene and oxygen. AS a result, it has been found that in the catalyst essentially comprising (a) palladium and (b) at least one compound selected from heteropolyacids and salts thereof, for use in the process for producing acetic acid by reacting ethylene and oxygen, when (c) a vanadium element and/or a molybdenum element is added in a specific ratio, the catalyst obtained can have high activity and be reduced in the changes by aging as compared with those obtained by conventional processes. The present invention has been accomplished based on this finding.
More specifically, the present invention (I) provides a catalyst for use in producing acetic acid, which is used in the process for producing acetic acid by ethylene and oxygen, wherein the catalyst comprises a support having supported thereon (a) palladium, (b) at least one compound selected from the group consisting of heteropolyacids and salts thereof and (c) a vanadium element and/or a molybdenum element, and the weight ratio of the compound of group (b) to the element of group (c) is in the range of the compound of group (b): the element of group (c) 1:0.0001 to 0.2.
The present invention (II) provides a catalyst for use in producing acetic acid, which is used in the process for producing acetic acid by reacting ethylene and oxygen, wherein the catalyst comprises a support having supported thereon (a) palladium, (b) at least one compound selected from the group consisting of heteropolyacids and salts thereof, (c) a vanadium element and/or a molybdenum element, and (d) at least one element selected from the group consisting of the elements belonging to Group 14, Group 15 and Group 16 of the Periodic Table, and the weight ratio of the compound of group (b) to the element of group (c) is in the range of the compound of group (b): the element of group (c) 1:0.0001 to 0.2.
The present invention (III) provides a catalyst for use in producing acetic acid, which is used in the process for producing acetic acid by reacting ethylene and oxygen, wherein said catalyst comprises a support having supported thereon (a) metal palladium, (b) at least one compound selected from the group consisting of heteropolyacids and salts thereof, (c) a vanadium element and/or a molybdenum element, and (e) at least one element selected from the group consisting of the elements belonging to Group 7, Group 8, Group 9, Group 10, Group 11 and Group 12 of the Periodic Table, and the weight ratio of the compound of group (b) to the element of group (c) is in the range of the compound of group (b): the element of group (c)=1 0.0001 to 0.2.
The present invention (IV) provides a process for producing the catalyst for use in producing acetic acid described in any one of the inventions (I) to (II).
The present invention (V) provides a process for producing acetic acid from ethylene and oxygen using a catalyst for use in producing acetic acid described in any one of the inventions (I) to (III).